The steel shank is designed to withstandconsiderable twisting force in proportion to its size,and the tip of the blade is hardened to keep it fromwearing.Standard screwdrivers are classified by size,according to the combined length of the shank andblade. The most common sizes range in length from2 1/2 to 12 inches. There are many screwdriverssmaller and some larger for special purposes. Thediameter of the shank, and the width and thickness ofthe blade are generally proportionate to the length, butagain there are special screwdrivers with long thinshanks, short thick shanks, and extra wide or extranarrow blades.When using a screwdriver, you should select theproper size so that the blade fits the screw slotproperly. This prevents burring the slot and reducesthe force required to hold the driver in the slot. Keepthe shank perpendicular to the screw head (fig. 1-48).RECESSEDRecessed screws are now available in variousshapes. They have a cavity formed in the head andrequire a specially shaped screwdriver. The clutch tip(fig. 1-47) is one shape, but the more common includethe Phillips, Reed and Prince, and newer Torq-Settypes (fig. 1-49). The most common type of screwfound is the Phillips head.This requires aPhillips-type screwdriver (fig. 1-47).Phillips ScrewdriverThe head of a Phillips-type screw has a four-wayslot into which the screwdriver tits. This prevents thescrewdriver from slipping.Three standard-sizedPhillips screwdrivers handle a wide range of screwsizes. Their ability to hold helps to prevent damagingthe slots or the work surrounding the screw. It is apoor practice to try to use a standard screwdriver onFigure 1-48.-Positioning screwdrivers.Figure 1-49.-Comparison of Phillips, Reed and Prince, andTorqSet screwheads.a Phillips screw, because both the tool and screw slotwill be damaged.Reed and Prince ScrewdriverReed and Prince screwdrivers are notinterchangeable with Phillips screwdrivers. Therefore,always use a Reed and Prince screwdriver with Reedand Prince screws, and a Phillips screwdriver withPhillips screws, or a ruined tool or ruined screwheadwill result.To distinguish between these similar screwdrivers,refer to figure 1-50.The Phillips screwdriver has about 30-degreeflukes and a blunt end, while the Reed and Prince has45-degree flukes and a sharper, pointed end. ThePhillips screw has beveled walls between the slots; theReed and Prince, straight, pointed walls. In addition,the Phillips screw slot is not as deep as the Reed andPrince slot.Figure 1-50.-Matching cross-slot screws and screwdrivers.1-29